.square, .circle {
    width: 100px;
    height: 100px;
    display: inline-block;
}


.circle {
    border-radius: 50%;
}


.red {
    background-color: red;
}

.yellow {
    background-color: yellow;
}


#container {
    background-color: lightgray;
    background-image: url('background.jpg');  
    background-size: cover;  
    background-position: center; 
    background-repeat: no-repeat;  
    width: 300px;
    height: 300px;
    margin: 0 auto;
    text-align: center; 
}